What age does middle age really start?

I’ve always thought it was like 40. I could be wrong. I’m 33 in a half about to turn 34 in November so I’m definitely not a young young adult anymore. I feel like it but still. I looked it up and it said 40-60 but some say 35 starts Middle age. Damn I’m not that far. 😳
If that’s true then I have a year in a half until I’m middle age but I know you can’t always believe everything you read or hear on the web. I’m just curious.
What age does middle age really start?
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